Conventionally, as a raw material for a blast furnace, there have been used agglomerated ores such as nonfired pellets and briquettes of 8 to 16 mm in diameter which are produced as follows: iron containing dust and coal containing dust recovered from various dust collectors in an iron works are blended to prepare a mixture, a cement-based aging binder is added to the mixture, and the mixture thus obtained is kneaded and formed. In this current production method of nonfired agglomerated ore, there is a problem that water of crystallization and a few % of adhesive water are contained since the hydration reaction based on a cement-based binder is invoked to ensure the product strength. Consequently, there is an apprehension that reduction retardation will occur in the shaft of a blast furnace and rapid heating bursting will also occur in the 500 to 700° C. region in the blast furnace, and hence the used amount of the above mentioned raw material is restricted to the content of 3% or less in relation to the main raw material used for the blast furnace; thus, the quality improvement of nonfired agglomerated ores is demanded from the viewpoint of raising the recycling rate in an iron works. Additionally, it has been reported that carbon containing nonfired pellets exhibit better development of reduction as compared to so-called non-carbonous sintered ores, fired pellets, and green ores that are usual raw materials for blast furnace; however, the carbon contents of these pellets mostly amount to only a few percents as a result of actual utilization modes of various types of dust in iron making and restraint for blending, and there are few reports on the optimal carbon content from the viewpoint of the blast furnace operation.
The present invention provides a drastic improvement measure for improving the deterioration behavior of the above described cement-based nonfired agglomerated ores, including reduction retardation and rapid heating bursting, from the viewpoint of the blast furnace operation. More specifically, the present invention provides a production method of a nonfired agglomerated ore wherein a carbon containing nonfired agglomerated ore is produced which contains carbon in an optimal content for blending dust raw materials and has a high cold strength; thus the reduction stagnation in the thermal reserve zone and reduction reaction equilibrium zone, known as an aspect of the blast furnace process, is avoided to promote the reduction; and the carbon containing effect and the improvement of the substrate strength by the binder are positively brought into effect, and the rapid heating bursting in the blast furnace is thereby prevented.